1. Field of the Invention:
The present invention relates to television systems. More specifically, the present invention relates to systems for transmitting and receiving high definition television signals.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art:
Conventional television systems are characterized by 525 horizontal scan lines and a 4:3 screen width to screen height (aspect) ratio. As discussed in a side article in "High-definition television update" by Ronald K. Jurgen, in the April 1988 issue of IEEE Spectrum, vol. 26, no. 4, pp. 56-62, in 1941, the Federal Communications Commission (FCC) adopted the National Television System Committee (NTSC) standard for the transmission of black and white television. It also allocated space for commercial television. In 1953, the NTSC standard was modified to add color information. In 1984, it was modified again to add stereo sound information. Although the standard has served the public well for nearly 50 years, certain defects limit its audio and video quality. Some of the defects are inherent, but others are the result of adding color information to the transmitted signal without increasing its bandwidth. In describing the defects, the FCC noted that viewers obtain a greater sense of realism and involvement, as well as an illusion of depth, not just from a better picture, but from a wider display, one that is a better match to the dimensions of the human field of vision than the 4:3 aspect ratio of conventional television systems. Further, the limited horizontal, vertical, and luminance resolutions of NTSC television results in pictures that are less sharp and bright than in movie theaters, while audio quality is limited in comparison with the sound produced by today's compact disks. Television viewing conditions usually limit contrast intensity ratios to about 60:1 even though about 250:1 may be transmitted.
Thus, a new standard for audio and video television is being considered. This promising new standard is referred to as high definition television or HDTV. High definition television is characterized by 900 to 1200 horizontal scan lines, more resolution across each scan line, and an aspect ratio of approximately 5:3. Hence, high definition television systems will provide as much as 5 times more visual information. The resulting video image quality is expected to be as good as that obtained from 35 mm film, while the resulting audio is expected to be as good as that obtained from digital audio disks.
While there are many current proposals for HDTV, there are also many problems. Terrestrial transmission, i.e., excluding cable and satellite transmission, is currently limited in bandwidth by the NTSC standard. That is, a single NTSC channel currently occupies only 6 megahertz of bandwidth while some HDTV proposals would require as much as 10 megahertz per channel. Adoption of such proposals for the HDTV standard would require the FCC to reconfigure the American broadcasting spectrum. This may require many TV owners in the United States, Canada, Japan and Latin America to buy a new and probably expensive TV set.
As discussed in "The Push for a Sharper Picture" by H. Brody, in the April 1988 issue of HIGH TECHNOLOGY BUSINESS, vol. 8, no. 4, pp. 25-29, some proposed systems are compatible with existing NTSC television sets. Unfortunately, these systems either do not provide a quality HDTV system or require additional channels or are exceedingly expensive for the average consumer.
Hence there is a need in the art for an inexpensive, bandwidth conservative high definition television system which is compatible with the present NTSC standard.